The ontogeny of the bile acid conjugaton and sulfation mechanisms will be investigated in fetal and post natal life. Post natal dietary factors, specifically the availability of dietary taurine, will be evaluated to determine their influence on bile acid conjugation patterns in preterm infants. The latter studies will utilize recently developed high performance liquid chromatographic techniques for the identification and quantification of bile acid conjugates, and GLC-mass spectroscopic analysis for confirmation of bile acid structure and for isotope ratio determinations. Non radioactive 13C labelled bile acids will be used as tracers in order to investigate the interrelationships between bile acid conjugation patterns and the regulation of bile acid synthesis rates and bile acid pool size. These findings will all be interpreted relative to their influence on intraluminal bile acid concentrations during meals and on the absorption and utiization of dietary lipid in the preterm infant. The ontogeny of hepatic sulfotransferase activity for bile acids and for pharmacological agents will be characterized in an animal model system. This process is a central mechanism for the conjugation and excretion of potentially toxic lipophilic compounds in bile and will be investigated as an alternate excretory pathway in children with defects of bile acid synthesis, or with cholestatic liver disease or biliary atresia. Finally, 13C methacetin will be utilized as a probe to evaluate the development of both hepatic microsomal functions and hepatic sulfotransferase activity in an animal model and in children with liver disease.